What is LiDAR (Abbreviation for Light detection and ranging), how does it work?
Steve Bodecker: A surveying device sends laser beams from an airplane or a helicopter towards the ground. LiDAR is mostly used over a large area. It now depends on the data that is reflected and registered by a transmitter in the aircraft. Laser beams cannot penetrate matter, they are only reflected. The data that comes back first shows the scan of the outermost surface. Houses or the forest are recorded with the tree canopy. For us archaeologists, however, the “last pulse”, the final answer, is decisive. These are the laser beams that have reached the area of the ground. This also works with very dense vegetation – because of the high frequency of rays. Even with a dense tree population, some rays always find the ground. Here you get a terrain model of areas that are forested. After processing on the computer, the result is a forest area without a forest. Roman maneuvers are easy to recognize on it. For archeology, this new perspective was a breakthrough in many areas. Unfortunately, the technology works less well on arable land, where the findings are mostly leveled.
How long has LiDAR been used in archeology?
The technology of laser scans from the air was used more and more around the year 2000. The first major measurements were carried out in Bavaria. There was an expansion in the early 2010s. The state survey offices have collected data across the board with LiDAR and have made most of them freely accessible online. With free software they can be viewed and analyzed by anyone on the net. Two portals can perhaps be named as examples: for NRW Tim online, there you can switch on the laser scan under “Terrain hillshading”; for Bavaria the Bavaria Atlas, there you can find the laser scan under “Overlays> Terrain relief”. Some federal states offer this data free of charge, some, such as Rhineland-Palatinate, on request. The usability of these viewers is actually very intuitive. You can also switch on various historical maps, especially from the 19th century, and go on a “journey through time”. Sometimes you can only see a castle complex today as a relief in the laser scan, but you can still see the intact condition on old maps.
The data is updated every four or five years. In the meantime, since around 2015, the resolution of the scans has been so high that from an archaeological point of view, an improvement can hardly be made.
What were significant discoveries – worldwide and in Germany?
There were spectacular images of Aztec and Mayan sites in the jungle. Whole cultural landscapes were made visible here. There were also important discoveries in Germany; in North Rhine-Westphalia, for example, there were many Roman training camps along the Lower Germanic Limes. A typical example: In the hinterland of Bonn, in the Kottenforst, a Roman camp had already been known, but a look at the laser scan showed four to five more directly next to it. We wondered why they weren’t discovered earlier. On the spot, however, you can see that the vegetation is so dense that it was not possible. We also found a whole cluster of camps in Xanten and Wesel. Suddenly a whole landscape of maneuvers spread out.
Still relatively new and spectacular, perhaps also exemplary of the advantages of the open data policy: In 2017, a committed lay researcher reported a suspected site of a Roman camp to the Rhineland Regional Council (LVR). Indeed, he had clearly found a huge Roman camp. Unfortunately it was in the field of my colleagues in Westphalia. It has now been verified by excavations and is considered the easternmost camp in Westphalia known from the Roman army and is located directly on the Teutoburg Forest near Bielefeld. It will certainly be discussed whether it possibly played a role in the context of the Varus defeat. But the laser scan cannot clarify that, it still needs the excavation.